What the hell happened with Heath Ledger?

O.K So I'm I'm a little slow to jump on the bandwagon but I just saw Dark Knight. Now I knew about Heath Ledger dying and it was sad but after I saw the film. Woah. So all these people were saying that Ledger had talked to Nicholson but I did some research and found out that that is not true. I mean the Joker Performance was amazing in every sense of the word. So can someone fill me in on the eerie performance and his death. I read that he was getting consumed by the role, but I can't sift through all crap from the truth. Some tell me what the hell happened!